The purpose of pretreatment is to get a good coating. Because the above stamping parts will have grease, oxide rust, dust, rust and corrosives on the surface during manufacture, processing, handling and preservation, if not removed, it will directly affect the performance and appearance of the coating film, so pretreatment occupies a very important place in the coating process. Important position. In our luggage hardware industry, baking varnish is the key link of luggage hardware. Here we introduce the baking varnish technology of Chino hardware.
1. Substrate:
The base material of the hardware baking varnish is
Stamping or sheet metal of cold rolled steel sheet
Stamping or sheet of galvanized steel sheet
Magnesium alloy stamping parts or sheets
Aluminum alloy stamping parts or sheets
But the baking process is quite different.
2. Hardware painting process:
Pretreatment - > Drying - > Primer Coating - > Baking - > Topcoat Coating - > Baking - > Inspection - > Packaging
3. Surface pretreatment:
(1) 1 oil removal; 2 water washing; 3 rust removal; 4 water washing; 5 table adjustment; 6 water washing; 7 phosphating; 8 water washing; 9 water washing; 10 drying;
(2) Purpose and importance of pretreatment:
The purpose of pretreatment is to get a good coating. Because the above stamping parts will have grease, oxide rust, dust, rust and corrosives on the surface during manufacture, processing, handling and preservation, if not removed, it will directly affect the performance and appearance of the coating film, so pretreatment occupies a very important place in the coating process. Important position.
(3) Significance of pretreatment:
Pretreatment, coating and drying are the three main processes of the coating process. Pretreatment is the basic process, which has an important impact on the quality, service life and appearance of the coating.
After degreasing, rust removal, phosphating and other processes, the workpiece surface is clean, uniform and oil-free.
1. Degreasing:
The main oils are mineral oil, grease, animal and vegetable oils, such as grease touched by hand during operation and handling, which seriously reduces the adhesion of most coatings, affects their drying, and also reduces the hardness and gloss of coatings.
The main alkali is NaOH, NaHCO3 and so on. Special degreasing powder can be purchased and then prepared into water solution. The saponification of soap.
2. Washing
Rinse with clear water to avoid contamination of the solution in the previous process to the next one. Clear water must be alive.
3. Derusting
Yellow rust can promote the spread of corrosion products under the coating and make the coating lose its shielding and impermeability. In high temperature and humidity conditions, it can lead to early damage of coatings and metals, loose rust, poor adhesion, and can peel off with coatings.
There are many methods for rust removal, such as alkali solution method, acid solution method, mechanical method, electrolysis method, etc. The common method is alkali solution method. Removal of oxide skin and rust marks on the surface of workpiece by chemical solution is usually done with sulfuric acid and oxalic acid. It can also be assisted by ultrasonic cleaning.
4. Tables (neutralization)
The abbreviation of surface adjustment: remove the excess alkali (or acid) on the surface of rust removal process with acid (or alkali) solution, and adjust the acidity to neutrality as far as possible, that is, PH value = 7;
Function: Speed up phosphating speed, refine phosphating crystallization, increase the crystallization point of phosphating;
5. Phosphating
Phosphating is the central link of pre-coating treatment. Metal workpieces are treated with orthophosphate solutions of manganese phosphate, zinc and cadmium phosphate to form an insoluble phosphate protective film on the surface of the workpiece. The phosphating film system formed has compact structure of fine holes, enlarges the surface area of the workpiece, and enlarges the contact area of the coating. The favorable interpenetration between the phosphating film and the coating greatly improves the adhesion of the organic coating to the workpiece.
The phosphating film formed by phosphating is a stable and non-conductive isolation layer, which changes the metal surface from a good conductor to a bad conductor, inhibits the formation of micro-batteries and effectively prevents the corrosion of coatings.
The common methods of phosphating are divided into high temperature phosphating (70-90 C), medium temperature phosphating (50-70 C) and normal temperature phosphating (20-30 C).
Phosphating film is usually black.
6. Drying
The above pretreatment process is basically carried out in the flume. And there is a time limit for each process. Dry the water and prepare to paint.
IV. Pre-hanging Quality Inspection
Before on-line inspection of unpainted workpieces is carried out; a large part of the unpainted products are unpainted, and it is necessary to check whether they can be sprayed directly or to remove the old paint; methods of removing the old paint, solvent immersion cleaning or removal with special paint remover.
5. Grinding
Non-essential process, remove surface granular impurities and increase a certain roughness to increase paint adhesion;
First time: 400_water sandpaper
Second time; 800_sandpaper or finer
Sixth, hanging up
The product is hooked on the hanger and the hanger conducts electricity and moves along the pipeline; the hanger should be a conductor and need to be grounded (for electrostatic coating); the hanger is generally customized according to the different characteristics of the product; the number is large, and the whole pipeline is used in turn.
Seventh, blowing dust
Removal of surface dust, chips, etc. Compressed air; Electrostatic precipitator gun; Flame combustion;
VIII. Manual Spraying
Pre-spraying the lower potential (such as shadows, concaves, etc.) before automatic spraying, but it is also a necessary choice when there is no automatic spraying equipment. The efficiency is not high, the productivity is limited, there are many unstable factors, the bad rate is high, and the thickness of the paint film is uneven.
